Silva Et Al 2009

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The primary purpose of this paper is to present the main water

mass properties (temperature, salinity, dissolved oxygen, nutri-

ents) and to describe some important features of their long-itudinal and latitudinal distributions off the coasts of Chile and

Peru. This paper also presents the vertical distributions (up to

1500 m) of the water masses, their participation in the sea water

mixture, and their physical and chemical characteristics. Due to

the presence of an anomalous NO3:PO4

3 molar ratio compared to

Redfields, the nitrate deficit, in terms ofN* (Deutsch et al., 2001),

is proposed as a chemical water mass tracer for the ESSW off

central and southern Chile.

2. Methods

The study area is located off the coasts of Peru and Chile from

101S to 511S and from the coast to 1001W. Since no singleoceanographic cruise covered this entire area, we based our

oceanographic analysis on three expeditions. Two latitudinal

sections (perpendicular to the coast) were selected, one

2500 km in length at 281S and the other 2000 km at 431S. A thirdlongitudinal section, 5000 km in length, was defined along the

coast off Peru and Chile (Fig. 1). The latitudinal sections included

the easternmost stations of the transpacific sections of the

SCORPIO cruise (Sta. S87S106 in May 1967 and Sta. S62S78 in

June 1967). The longitudinal section, running almost parallel to

the coast, used some stations from the KRILL Leg 4 cruise (Sta.

K28, K30, K33, K34, K35, K37, K40, K42, K45; June 1974), covering

the area between 101S and 361S; an additional station from

section 431S of the SCORPIO cruise (Sta. S77; June 1967) and two

stations from the PIQUERO cruise (Sta. P33, P48; June 1969)

expanded the longitudinal section to 511S (Fig. 1). This composite

longitudinal section is the first coastal section done at distances

shorter than 250 km off the coast of Peru and Chile, from Callao

to the Strait of Magellan. Data from the PIQUERO andSCORPIO cruises were taken from the respective Data Reports

ARTICLE IN PRESS

Fig.1. Geographic position for oceanographic stations of the KRILL, SCORPIO, and PIQUERO expeditions. Inset shows the main currents off Peru and Chile: ACC Antarctic

Circumpolar Current; HC Humboldt Current; CHC Cape Horn Current; PC Peru Countercurrent; PCU PeruChile Undercurrent.

N. Silva et al. / Deep-Sea Research II 56 (2009) 10041020 1005

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(Scripps Institution of Oceanography, 1969, 1974); data from the

KRILL cruise were provided by Dr. T. Antezana, Universidad de

Concepcion.

We think that the time gaps in the combined sections did not

invalidate the results and conclusions of this study since the

variables mapped showed spatial continuity regardless of the

time differences. Moreover, all cruises were performed during

years without either El Nino or La Nina events (NOAA, 2006).Therefore, there were no warm/cold periods that could bias our

comparison. All three cruises recorded the temperature with

reversing thermometers and water samples for chemical analyses

were taken with reversing bottles at standard depths. Chemical

analyses were done as follows: salinity using an induction

salinometer, dissolved oxygen using the Winkler method modified

byCarpenter (1965), and nutrients by visible spectrophotometry

(Strickland and Parsons, 1972). The percentage of the saturation of

dissolved oxygen was calculated using Weiss (1970) saturation

concentrations. The mixed layer depth for a given oceanographic

station was considered to be the deepest common depth of the

isothermal and isohaline layer, with both isolayers present

simultaneously.

In order to analyze the distribution of water properties, thefollowing data were mapped for each transect: temperature,

salinity, density (sy), dissolved oxygen, nitrate, nitrite, phosphate,

and silicate. These data were analyzed up to 1500 m, the common

maximum depth for the three cruises.

Water mass distribution was analyzed usingTSdiagrams for

the oceanographic stations and the mixing triangle method

(Mamayev, 1975). According to the mixing triangle method, in

order to calculate the percentages of the mixing ratio, it is

necessary to define the different thermohaline indices (T, S) that

are typical for each water mass in a given triangle. For the area off

Peru and Chile, TS pairs from Silva and Konow (1975)

corresponding to a winter period were used (Table 1;Fig. 2).

Adjustments were made when theTSpair of a specific record

was not included in one of the respective mixing triangles,

whether due to higher/lower temperatures or salinity. Deviations

from higher temperatures were corrected by holding the salinity

value constant and decreasing the temperature until theTSpair

fell into the nearest triangle. Deviations due to salinity were

corrected by holding the temperature value constant and adjust-

ing the salinity. This technique is considered valid as long as the

deviated TS points could respond to a local warming and/or

evaporation situation. Moreover, the thermohaline index selected

corresponds to a single TS pair for a given water mass and

represents a whole group ofTSpairs from the area generating the

water mass, all of which are equally valid for representing it.

The nitrate deficit, defined as N* nitrate16*phosphate+2.9

mmolkg1 according to Deutsch et al. (2001), was used as a

chemical water mass tracer. Section 281S showed some nutrient

values below 600m that did not follow a smooth vertical

distribution pattern and, therefore, were not considered for N*

computations.

3. Results and discussion

3.1. Water masses off Peru and Chile (101S511S)

TheTSdiagrams of the three sections in the study area (Fig. 2)

suggest the presence of five water masses that, according toSilva

and Konow (1975), are: Subtropical Water (STW), Subantarctic

Water (SAAW), Equatorial Subsurface Water (ESSW), Antarctic

Intermediate Water (AAIW), and Pacific Deep Water (PDW). Of

these, STW and SAAW are surface waters, the former found mostly

in the north (o231S) and the latter in the south (4281S) of the

study area.

Analyses of water mass characterization and distribution offthe coasts of Peru and Chile have been based mostly on the

determination of the presence/absence of conservative properties.

On occasion, semi-conservative properties such as dissolved

oxygen or nutrients below the surface layer have also been used

(Gunther, 1936;Wyrtki, 1967;Zuta and Guillen, 1970;Sievers and

Silva, 1975).

The mixing triangle method offers advantages in the use of the

qualitative spatial distribution of the physical and chemical

properties of water masses, as it presents a quantitative view of

the spatial distribution of the water masses being analyzed.

Johnson (1973) studied the distribution of AAIW in the South

Pacific along 1601W between Ecuador and 601S;Silva and Konow

(1975) analyzed the water mass distribution along the coasts of

Peru and Chile (10361S); and Cucalon (1983) showed how thewater masses were distributed off the coast of Ecuador (along

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Table 1

Water masses and their thermohaline indices (T,S) for each of the mixing triangles

used to compute water mass participation in the sea water mixture (Silva and

Konow, 1975).

Triangles Water masses T(1C) S

STWSAAWESSW Subtropical Water (STW) 20.0 35.2

Subantarctic Water (SAAW) 11.5 33.8

Equatorial Subsurface Water (ESSW) 12.5 34.9

SAAWESSWAAIW Subantarctic Water (SAAW) 11.5 33.8

Equatorial Subsurface Water (ESSW) 12.5 34.9

Antarctic Intermediate Water (AAIW) 3.0 34.0

ESSWAAIWPDW Equatorial Subsurface Water (ESSW) 12.5 34.9

Antarctic Intermediate Water (AAIW) 3.0 34.0

Pacific Deep Water (PDW) 1.75 34.68

Fig. 2. TS diagram for selected KRILL, SCORPIO, and PIQUERO stations off Peru and

Chile and mixing triangles. (STW Subtropical Water; SAAW Subantarctic

Water; ESSW Equatorial Subsurface Water; AAIWAntarctic Intermediate

Water; PDW Pacific Deep Water).

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821300W, between 21N and 31S) and how they were affected by the

1976 El Nino.

As the water masses move in or out of the study area, flowing

at their respective density levels, they mix with each other. This

mixing erodes the water masses until, at a given latitude/

longitude, both the conservative and semi-conservative charac-

teristics erode completely, losing their identity; at this point, the

water mass is no longer considered to exist.The application of this method resulted in three mixing

triangles for the five water masses in the study area (Fig. 2;

Table 1). The results were used to map percentages of participa-

tion, or mixing ratios, in the water mass mixture equal to or

greater than 50% of each water mass; that is, where it was

predominant. In some locations, where pertinent, lower mixing

ratio values were used to show remnants of a given water mass.

3.2. Subtropical and Subantarctic Water

In general, the surface layer over the thermocline

(o100150 m) in the longitudinal section (10511S) increased in

temperature (from 10 to 191

C) and salinity (from 33.5 to 35.1)towards the north (Figs. 3A and 4A). In the northern section

(281S), both temperature and salinity increased toward the west

(from 13 to 20 1C; from 34.4 to 35.5) (Figs. 3B and 4B). In the

southern section (431S), the temperature remained around 13 1C

throughout the section and salinity increased toward the west

(from 33.5 to 34.0) (Figs. 3C and4C). Surface density, in terms ofsy, showed latitudinal/longitudinal differences in the study area,

being less dense in the north (25.025.2) than in the south

(25.425.8) (Fig. 5AC). These general characteristics are typical of

the eastern border of the South Pacific Gyre. The northern area of

the gyre is associated with the high-pressure areas of the

Subtropical Pacific Anticyclone, on average, receiving more solar

radiation and having greater evaporation. This causes an increase

in water temperature and salinity, giving rise to the formation of

STW in the surface layer (Wyrtki, 1968). The southern area of the

gyre receives, on average, less solar radiation and is affected by the

subpolar low-pressure system, associated with high rates ofoceanic precipitation. This, along with the Coastal and Andes

mountain ranges, acts as a topographic barrier, increasing local

terrestrial precipitation, contributing to the formation of pluvial

regime rivers, and favoring the accumulation of glacial snow and

ice, which eventually melt and reach the sea through nival regime

rivers. Thus, the areas adjacent to the southern Chilean fjords and

channels have low temperatures and salinity (Silva and Neshyba,

1980;Rojas and Silva, 1996;Davila et al., 2002), giving rise to the

formation of SAAW in the surface layer (Wyrtki, 1968).

In the longitudinal section, STW was found in the surface layer

and was about 50 m thick from 101S to 241S; STW participation in

the sea water mixture was between 50% and 90% (Fig. 6A). In the

281S section, west from 781W, STW participation was between

50% and 99%, and its thickness increased from 100 m at 791W to200m at 1001W (Fig. 6B). To the east, in the coastal area, STW

participation in the mixture did not surpass 50% and only reached

around 4050% in a few places (Sta. 89, 91, 93). In the 431S section,

STW was not present, except at some isolated points, with

remnants less than 12% (Sta. 63, 62) (Fig. 6C).

In the longitudinal section, SAAW was preponderant (450%) as

a surface water mass stretching from 521S to 281S with a thickness

of about 80100m (Fig. 6A). The SAAW core began to sink around

351S, at the Subtropical Convergence, as a tongue centered on

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Fig. 3. Vertical distribution of temperature (1C). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 281S(SCORPIO expedition), and (C) latitudinal section off 431S (SCORPIO expedition).


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50 m, moving northward between surface STW and subsurface

ESSW, generating a shallow salinity minimum (SAAW-ShSM). The

SAAW north of 251S was highly eroded and only identifiable to

201S as a remnant (10%) in the water mass mixture (Figs. 4A and

6A). In the 281S section, SAAW was a continuous subsurface

tongue between the coast and 911W, centered on 50m in the

coastal area and on 200 m at 901W with 5080% participation in

the mixture (Fig. 6B). The SAAW was located between the STW

and the ESSW, except in the coastal area, where it reached the

surface, displacing the STW. Here, the position of the SAAW core

corresponded to that of the SAAW-ShSM (Figs. 4A and 6B).

Throughout the entire 431S section, SAAW was a 100120 m thick

surface layer, with between 50% and 99% participation in the

mixture (Fig. 6C).

The surface water masses (STW, SAAW) include the mixed

layer, which was deepest in the northwestern end and shallo-westsometimes absentin the southeastern end. All along the

longitudinal section, the mixed layer appeared as a layer of

variable depth, with no defined increase/decrease pattern,

fluctuating between 20 m (Sta. K33) and 80 m (Sta. K40) (Figs. 3A,

4A,5A, and6A). To the north, the STW temperature in the mixing

layer was 18 1C, salinity was 35.0, and sywas 25.2. To the south,

the SAAW temperature was 12 1C, salinity was 33.9, and sy was

25.7. Dissolved oxygen in the surface layer (o10 m) increased

from north to south from 4.6 to 6.2 mLL1 (Fig. 7A) due to the

greater dissolution capacity of the colder, less saline waters

(Figs. 3A,4A). Thus, dissolved oxygen saturation remained around

90110% along the transect. A homogeneous layer of nutrients

(nitrate, nitrite, phosphate, silicate), similar in thickness to the

mixed layer at the different stations, showed higher concentra-tions to the north of the section (416mM nitrate; 41.4mM

phosphate; 45mM silicate) and lower values in the center and

south (o8mM nitrate; o1.0mM phosphate; o5mM silicate)

(Figs. 8A,10A, and11A). Nitrite was less than 0.1mM throughout

the mixed layer of the longitudinal section (Fig. 9A).

The 881W WOCE P19C section (Tsuchiya and Talley, 1998;

Talley, 2005a), between 101S and 401S, presented a uniform mixed

layer of about 40 m thick, with comparatively high temperatures

and salinities (1423 1C; 3436) and low nutrient concentrations

(o5mM nitrate; o0.5mM phosphate; o0.1mM nitrite; o2mM

silicate). These low nutrient values are typical of the central gyres

where because of the pycnocline, contribution of nutrients to the

surface layer becomes difficult. These conditions were not

observed in our longitudinal section, which had relatively low

temperatures and high nutrient values due to the fact that our

section is closer to the coast (i.e., 100300 km). Therefore, it is

closer to coastal upwelling areas that carry nutrients to thesurface (Codispoti, 1981; Ahumada et al., 1991; Morales et al.,

1996, 2001;Silva and Valdenegro, 2003).

In the 281S section, the mixed layer increased gradually in

thickness, temperature, salinity, and density toward the west

(Figs. 3B, 4B, and 5B). To the east, this mixed layer was around

40 m thick, with a temperature of 17 1C, salinity of 34.4, and syof

25.0; part of it was associated with SAAW and part with STW

(Figs. 3B,4B,5B, and6B). To the west, the mixed layer thickness

was around 120m, with a temperature of 20 1C, salinity of 35.5,

and sy of 25.2 associated with STW. In the 281S section of the

SONNE 102 cruise (June 1995; Leth et al., 2004), the depth,

temperature, and salinity of the mixing layer were similar to those

of the SCORPIO cruise (June 1967). This coincidence can be

explained by the fact that all oceanographic samplings were donein the same climatic season (winter) and the cruises were

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Fig. 4. Vertical distribution of salinity. (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 28 1S (SCORPIO

expedition), and (C) latitudinal section off 431S (SCORPIO expedition).


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performed during normal climatic years with no El Nino/La Nina

events (NOAA, 2006). Nevertheless, it is important to keep in

mind the 38-year difference between the two cruises.

Dissolved oxygen in the 281S section was practically homo-

genous (5 m L L 1), covering greater depths than those of the

mixed layer throughout the entire section (Fig. 7B). West of 781W,

the homo-oxic layer was found at depths nearly double those of

the mixed layer, implying a well-oxygenated layer around 200 m

depth in the oceanic area, with saturation values between 72% and

106%. Nutrients were also found as a homogenous layer with

thicknesses similar to those of dissolved oxygen. Nonetheless, and

unlike dissolved oxygen, nutrient concentrations were low

(o4mM nitrate; o0.1mM nitrite; o0.5mM phosphate; o5mM

silicate) and, in some cases, nitrate and silicate concentrations

were below the detection limit of the chemical analyses (Figs. 8B,

9B,10B, and 11B). East of 781W, the homogenous layer of highdissolved oxygen and low nutrients was thinner, similar to the

mixing layer. Sections 281S of the SONNE 102 cruise (Leth et al.,

2004) and 321S of the WOCE P6 cruise (Wijffels et al., 2001;Talley,

2005b) revealed vertical distributions of dissolved oxygen and

nutrients similar to those of the SCORPIO cruise, indicating that

these are permanent characteristics of the area.

In the 431S section, the SAAW mixed layer thickness was

around 50 m depth in the east and 60 m in the west (Fig. 6C);

therefore it was shallower than in the 281S transect (Fig. 6B). To

the east of the section, the mixed layer had temperatures around

131C, salinity of 33.5, and syof 25.4. To the west, the temperature

was around 12 1C, salinity was 33.9, and sywas 25.7 (Figs. 3C,4C,

and5C). In the 431S section of the SONNE 102 cruise, the depth,

temperature, and salinity of the mixed layer were similar to thoseof the SCORPIO cruise; as in the 281S section, this can be explained

by sampling that was done in the same climatic season, although

38 years apart.

The SAAW off the southern end of South America reaches as far

as 901W (Fig. 6C). This agrees with the findings of Reid (1969),

Silva and Neshyba (1980), andDavila et al. (2002). According to

Deacon (1977), SAAW is transported westward by an anticyclonic

flow, giving rise to a low-salinity tongue toward the west. Later

Neshyba and Fonseca (1980) presented additional information

about this; nevertheless, conclusive evidence on a westward

counter flow is still lacking.

Dissolved oxygen in the SAAW of the 431S section was

practically homogenous (6mLL1) and deeper than the mixed

layer throughout the entire section (Fig. 7C). This implies a well-

oxygenated layer around 100 m (coastal) and 200 m (oceanic)

deep, with saturation values between 85% and 105%. Nutrients

were distributed in a homogenous layer, similar in thickness tothe mixed layer, with relatively high nitrate (812mM) and

phosphate (0.61.0mM) and low nitrite (o0.1mM) and silicate

(o5mM) concentrations (Figs. 8C,9C,10C, and11C).

3.3. Shallow salinity minimum

Gunther (1936)first observed the SAAW-ShSM off the coasts of

Chile and Peru and explained it as a result of low-salinity SAAW

sinking in the Subtropical Convergence, then continuing north to

101S.Wyrtki (1967)offered a similar explanation of SAAW moving

northward under STW, which initiates around 351S at the

Subtropical Convergence. Because the east Pacific and Atlantic

present similar SAAW-ShSMs,Reid (1973a)considered them to becommon characteristics of eastern boundary currents. Later works

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Fig. 5. Vertical distribution of density (in terms of sigma-t). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal

section off 281S (SCORPIO expedition), and (C) latitudinal section off 431S (SCORPIO expedition).


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proposed that the shallow salinity minimum in the eastern South

Pacific is produced by the subduction of low-salinity SAAW

directly in the thermocline near 371S; the SAAW-ShSM is then

carried north and west on the eastern edge of the South Pacific

Subtropical Gyre by the Humboldt Current or the Peru Current

(Reid, 1973a; Tsuchiya and Talley, 1998; Schneider et al., 2003;

Leth et al., 2004).

In our longitudinal section, the SAAW-ShSM was identified as

such beginning at around 341S and was centered near the base of

the thermocline (Figs. 4A and6A), coinciding with observations by

Tsuchiya and Talley (1998)for the 881W section (WOCE P19C) and

Schneider et al. (2003) for the shallow salinity minima distribu-

tions in waters off Chile and Peru. The SAAW-ShSM weakened as it

extended northward; salinity increased due to mixing with more

saline surface STW (S434.9) and subsurface ESSW (S434.8). This

saline minimum appeared as a finger or a tongue of lower salinityembedded in the thermocline and along sy26.2. The salinities of

the SAAW-ShSM increased from 34.3 (301S) to 34.8 (201S) and this

water mass was still distinguishable around 171S as an inflection

of the 34.9 isohaline to 100 m depth (Fig. 4A).

For the longitudinal 881W section,Tsuchiya and Talley (1998)

proposed double diffusion via salt fingering as a possible

mechanism acting to erode the SAAW-ShSM from above as it is

advected equatorward. Leth et al. (2004) proposed the same

explanation for the erosion of the SAAW-ShSM in the 281S section

of the SONNE 102 cruise. In these two works, the authors relied on

the Turner angle (Ruddick, 1983), which can be used to detect salt

fingerings. However, we were not able to compute Turner angles

for the sections used herein since we had bottle data spaced at

standard depths, which are not suitable for this computation, asare CTD continuous data.

Because the SAAW-ShSM depth coincides with the oxycline

and nutricline, the latter two characterize the SAAW-ShSM, with

comparatively low dissolved oxygen concentrations that are

embedded in the maximum vertical gradient of the oxycline

(14mLL1; 2060% saturation) and comparatively high nutri-

ents embedded in the nutricline (1220 mM nitrate; 2.22.6mM

phosphate; 520mM silicate) (Figs. 8A,10A, and11A).Leth et al.

(2004) considered it likely that this strong vertical gradient

indicated the boundary between the well-ventilated waters from

the south and the oxygen-poor waters from the north. These

authors also found high dissolved oxygen in the SAAW-ShSM and

a sharp oxygen gradient at its base. Instead, we think that the

waters of the SAAW-ShSM are characterized by intermediate

(4mLL1), at its upper boundary, to low (2mL L1) dissolved

oxygen concentrations at its lower boundary, due to its mixing

with the less oxygenated ESSW (o1mLL1), thereby ventilatingits upper part. This agrees with the proposal ofDe Pol-Holz et al.

(2007)for the ventilation of the ESSW off the coast of Chile.

In the 281S section, the SAAW-ShSM is distinguished by

salinities lower than 34.3, centered on 100m in the coastal zone

and on 200 m at 911W, its western boundary in our study (Figs. 4B

and6B). In the 281S section of the SONNE 102 cruise (Leth et al.,

2004), the SAAW-ShSM was identifiable by its salinities of less

than 34.3 from the coast to at least 861W, the western limit of this

transect. In the case of the 321S section of the WOCE P6 cruise

(Wijffels et al., 2001; Talley, 2005b), the SAAW-ShSM was

distinguishable by salinities less than 34.3 between the coast

and 941W; in both cases, as in the SCORPIO cruise, SAAW-ShSM

core depths were greater to the west. According toTsuchiya and

Talley (1996), the SAAW-ShSM can still be distinguished at 1351W(WOCE P17), indicating that, although their figures do not show

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Fig. 6. Vertical distribution of water mass percentages. (A) Longitudinal section off Peru and Chile (1052 1S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section

off 281S (SCORPIO expedition), and (C) latitudinal section off 431S (SCORPIO expedition). (STW Subtropical Water; SAAW Subantarctic Water; ESSW Equatorial

Subsurface Water; AAIW Antarctic Intermediate Water; PDW Pacific Deep Water).


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between the low nutrient SAAW and the AAIW, giving rise to a

nutrient maximum in the ESSW south of 281S, which diminishes

gradually until 481S due to mixing (Figs. 8A and 10A); south of

this point, it has not been observed (Silva, 1977; Silva and

Neshyba, 1980).

In the surface layer of the longitudinal section, nitrite

concentrations were less than 0.1mM, with occasional high

concentration maxima associated with the thermocline. These

maxima, which are called primary maxima, tend to fluctuate

between 0.25 and 0.75mM and are located around 75100 m.

Primary maxima are generated in the thermocline due to the

accumulation of extracellular products from plankton exudation.

Deeper in this section (150200m), between 151S and 281S,

nitrite presented two subsurface maxima with concentrations

greater than 6mM (Fig. 9A). These so-called secondary maxima

were associated with two cores of minimum nitrate concentra-tions (o16mM) (Fig. 8A). Denitrification processes in quasi-anoxic

environments (o0.2mLL1) decrease nitrate, which is used as an

oxidant for breaking down the organic material present, and

accumulate nitrite, which is produced in one of the intermediate

degradation steps (Brandhorst, 1959;Codispoti and Packard, 1980;

Anderson et al., 1982). These secondary maxima can surpass the

normal oceanic concentrations by one order of magnitude (i.e.,

47mM, Sta. K33, off 251S) and, on occasions, by up to two orders

of magnitude (i.e., 411mM, off 151S) (Codispoti and Christensen,

1985).

In the 281S section, the ESSW appeared as a continuous

subsurface tongue (440% ESSW) between the coast and 951W,

centered on 200 m in the coastal area and on 400 m in the west.

The ESSW, located between the SAAW-ShSM and the AAIW, had amixing ratio between 50% and 80% (Fig. 6B). The position of the

ESSW core in this section corresponded to that of the OMZ, unlike

the situation in the north of the longitudinal section, where the

OMZ was thicker than the ESSW.

The salinity maximum of the ESSW in the 281S section

stretched more or less continuously from the coast to 961W, with

three cores (434.6): one at the edge of the continental shelf,

another at 761W, and a third at 911W (Fig. 4B). The salinities of

these cores decreased and deepened toward the west, from values

over 34.8 at 200 m on the continental slope border to over 34.6

around 350 m at 911W.

The distributions of the subsurface dissolved oxygen minimum

and the nutrient maximum in the ESSW were similar in extension

and depth to those of the salinity maximum. Close to the

continental slope, dissolved oxygen concentrations were less than

0.5mLL1 and nutrients were greater than 32mM nitrate, 2.6mM

phosphate, and 20mM silicate (Figs. 7B,8B, 10B, and11B). Towardsthe west, dissolved oxygen increased to around 2 mLL1 and

nutrients decreased to 28mM nitrate, 2.4mM phosphate, and

15mM silicate at 851W. At 911W, a core of low dissolved oxygen

(o2mLL1) and high nutrient content (428mM nitrate, 42.6mM

phosphate, 420mM silicate) was associated with the most

western high salinity core, described earlier. The chemical

characteristics of this core correspond to ESSW, although, in this

case, the waters are not transported southward by the PCU, which

flows closer to the coast.

Leth et al. (2004) also observed two coastal cores with high

salinity and low dissolved oxygen, one closer to the continental

slope and the other centered on 761W. These authors indicated

that the more oceanic core could be caused by a poleward flow

separated from the more coastal PCU. The 281S section of theSONNE 102 cruise used by Leth et al. (2004) did not provide

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Fig. 8. Vertical distribution of nitrate (mM). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 281S

(SCORPIO expedition), and (C) latitudinal section off 431S (SCORPIO expedition).


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additional evidence for the presence of the oceanic core at 901W,

as no sampling was done west of 861W. LikeLeth et al. (2004), we

think that the core centered on 901W is also the result of a

poleward flow separated from the coastal PCU.

The 271S section of the CIMAR 5 Islas Oceanicas cruise

(OctoberNovember 1999) between the coast and 1101W also

presented three high salinity cores (434.5) associated with

the dissolved oxygen minima (o2mLL1). The core closest to

the continental slope spread farther west and the two more

oceanic cores differed in position from the SCORPIO and

SONNE 102 cruises, which were located at 871W and 961W,

respectively (Fuenzalida et al., 2000). The core closest to the

coast is associated with the PCU and the others with more

oceanic flows that also involve advection of the ESSW. In the 241S

section of the STEP I cruise (Wooster and Gilmartin, 1961;Wyrtki,

1963), two cores were observed where the ESSW participationwas more intense: one near the continental slope associated with

the PCU and the other oceanic (801W), associated with what

Wyrtki (1963) called the Peru Countercurrent, flowing south off

Peru and Chile.

In the sections 361S of the SCORPIO cruise (Reid, 1973b), 321S

of WOCE P6 (Wijffels et al., 2001), and 361S of SONNE 102 (Leth

et al., 2004), the ESSW presented three cores of high salinity

(434.6) and low dissolved oxygen content (o1mLL1): one on

the edge of the continental slope and two more oceanic. Never-

theless, neither the positions of the cores nor their intensities

coincided exactly, although the presence of a coastal core was a

permanent characteristic.

In the 431S section, the predominant participation of ESSW

(450%) was confined to about 50km from the edge of thecontinental slope (Fig. 6C). Nevertheless, its chemical character-

istics extended west up to 250 km as a wide coastal band centered

on 200 m depth, with weak maxima of salinity (434.3), nitrate

(428mM), phosphate (42.2mM), and silicate (420mM) and

a dissolved oxygen minimum (o4mLL1) (Figs. 4C,7C, 8C,10C,

and11C).

In both latitudinal sections (281, 431S), scant primary nitrite

maxima were observed; maxima in the southern section were

more frequent and had greater concentrations (40.5mM) (Fig. 9B,

C). Neither of the two had a secondary nitrite maximum, as found

in the northern part of the longitudinal section.

3.5. Antarctic Intermediate Water

The AAIW of the South Pacific, between 400 and 1200 m depth,

is generated to the north of the Polar Front, whether bythermohaline-driven circulation as proposed by Deacon in 1933,

or a wind-driven convergence formation mechanism as proposed

by Sverdrup in 1940 (inPiola and Georgi, 1982).

Later, McCartney (1977) proposed a modal water mass

mechanism, which he called Subantarctic Modal Water (SAAMW).

According to this author, SAAMW is formed in the eastern Pacific

off the southern coast of Chile through winter convection of SAAW

north of the Polar Front, giving rise to a relatively homogeneous

water column from the surface to 500600m depth. Later, in

summer, the upper portion of this homogeneous column warms

up and becomes stratified; remnants around 300600 m depth

present uniform characteristics or modes, generating a salinostad

and a pycnostad directly over the AAIW.

According toTsuchiya and Talley (1998), as the SAAMW flowstowards the equator in the 881W section (WOCE, P19), it can be

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Fig. 9. Vertical distribution of nitrite (mM). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 281S



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identified by its pycnostad (sy 26.927.1) until 281S; this

finding was not repeated in our longitudinal or latitudinal data

along 281S (Fig. 5A, B).Piola and Georgi (1982)indicated that, off

the southern coast of Chile, the characteristics of the SAAMW are

similar to those of the AAIW, suggesting that at least part of the

AAIW came from the SAAMW formed in this area.

As the salinostad and thermostad were practically absent in

our study area and since the AAIW and SAAMW in the area did not

differ much in their physical and chemical characteristics,

SAAMW was not considered to be a distinct water mass from

the AAIW. In applying the mixing triangle method, SAAMW did

not constitute a different water mass from the AAIW, but only a

variation of this water mass in this area that the method is not

able to discriminate. For this reason, we did not include SAAMW

in the analysis of characteristics of the water masses off the coasts

of Chile and Peru.In the longitudinal section, the AAIW extended preponderantly

from 521S to 271S, centered around 600 m (Fig. 6A). This water

mass began with a mixing ratio over 70% and a thickness of 900 m

at 521S, and was progressively eroded by mixing with more saline

ESSW and PDW. North of 271S, AAIW participation was between

20% and 50% in the water mass mixture, which made it

identifiable up to 101S, the northern extreme of the study area

(Fig. 6A).Johnson (1973), in an oceanic section along 1601W in the

South Pacific, determined 80% participation for the AAIW in the

water mass mixture at 521S. Extending northward, AAIW

participation at the equator was 50%; this is nearly 301of latitude

farther north than in our coastal-most study. None of the mixing

triangles used byJohnson (1973)included SAAW, even though he

identified it in his study area. Instead, he took into account thesurface Western South Pacific Central Water (WSPCW) in his

1601W transect. ESSW was also not included, since his section was

located almost at the center of the Pacific and this water mass is

only found on the edge of the eastern South Pacific.

The ESSW coastal-most water mass, as it is transported south

by the PCU, can erode the AAIW at a faster rate than the WSPCW,

producing the least equatorward penetration of the AAIW

observed herein and compared to Johnson (1973).

Salinity in the southern extreme of the longitudinal section

(52441S) increased rapidly in depth for the first 200 m, stabiliz-

ing between 500 and 700 m with values around 34.25 (salinos-

tad), and then increased again toward the bottom (Fig. 4A). A

pycnostad (27.027.1sy) was observed at this same level (Sta. P33,

P48). The salinity in this southern area does not constitute a

relative minimum as found farther north, because at this latitude

the saline maximum of the ESSW was totally eroded and had

lost its identity due to mixing. Thus, the comparatively higherAAIW salinities are present directly below the low SAAW salinities

(Fig. 4A).

The salinostad and pycnostad were not recorded north of 501S

in the longitudinal transect. Rather, only the characteristic salinity

minimum of the AAIW was observed as it moved equatorward

between the saltier ESSW (above) and the saltier PDW (below)

(Figs. 4A and 6A). Due to the above, the AAIW was observed

as a tongue of water with relatively low salinity, centered on

600 m in the south (34.25; 35401S), that became progressively

deeper (800 m) and more saline to the north (34.55; 10151S)

(Fig. 4A).

Since this water comes from the area north of the Polar Front, it

is comparatively high in dissolved oxygen and nutrients (Reid,

1965; Silva, 1977;Silva and Neshyba, 1980;Tsuchiya and Talley,1998). This can also be observed in the dissolved oxygen and

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Fig.10. Vertical distribution of phosphate (mM). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 281S



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nutrient sections from the cruises WOCE P19 at 861W

(Talley, 2005a) and WOCE P17 at 1381W (Talley, 2005c). At 501S,

off the Chilean coast, the AAIW is distinguished by its high

values of dissolved oxygen (46mLL1), nitrate (428mM),

phosphate (41.8mM), and silicate (415mM) (Figs. 7A, 8A,10A,

and11A).

As the AAIW flows northward between the ESSW and PDW,

comparatively poorer in dissolved oxygen and rich in nutrients, it

mixes progressively with them. Therefore, the AAIW appeared as a

tongue of water with a dissolved oxygen maximum that decreased

and a nutrient minimum that increased from south to north,

remaining perceptible until 28301S (O2 42mLL1; nitrate

o38mM; phosphate o2.8mM; silicate o25mM), at depths around

600m (Figs. 7A,8A, 10A, and11A).Reid (1973b)indicated that this

only occurs along the eastern boundary of the South Pacific, where

AAIW nutrient concentrations are high, as expected when wateroriginates north of the Polar Front. However, the nutrient

minimum observed in the vertical structure is due to the presence

of the nutrient-rich ESSW, which the PCU moves southward from

eastern subtropical areas.

North of 251S, the AAIW is no longer characterized by a

dissolved oxygen maximum and a relative nutrient minimum, due

to erosion by mixing. Only remnants of the saline minimum

(o34.55) remain, persisting weakly in the vertical structure to

101S, where its mixing ratio was less than 20% (Figs. 6A,7A,8A,

10A, and 11A). Moreover, north of 251S, the AAIW remnants

penetrate the deep part of the eastern South Pacific OMZ, poor in

dissolved oxygen (o0.2mLL1) and rich in nutrients (nitrate

444mM; phosphate 43.2mM; silicate 440mM), so that at this

point it is no longer distinguishable by a maximum/minimum ofthese properties.

In the section along 881W (WOCE P19C; Tsuchiya and Talley,

1998), the saline minimum of the AAIW was observed until 81S

with values less than 34.55, whereas the dissolved oxygen

maximum was observed until 231S with concentrations greater

than 3mLL1 (O24140mmol kg1). In the section along 1351W

(WOCE P17;Tsuchiya and Talley, 1996), the saline minimum of the

AAIW was observed until 51N with values lower than 34.55,

whereas the dissolved oxygen maximum was observed until 171S

with concentrations over 3 mL L1. In both transects, the nutrients

of the AAIW did not present a relative minimum as occurred in

the area of the eastern South Pacific where it is found below the

ESSW, as explained previously.

In the 431S section, the AAIW was present as a continuous

tongue between the coast and 1001W, centered on 600 m along

the entire section, with participation between 50% and 70% in the

water mass mixture. In the coastal area, the tongue was thinner(700 m) than in the oceanic area (1000m) (Fig. 6C).

In this southern section, the AAIW presented a salinostad

(34.25) and a pycnostad (27.027.1sy) centered on 500700 m

at only some stations (S64S72; Figs. 4C and5C). No salinostad

was observed at the coastal stations; rather the salinity minimum

was centered on the same depth (Sta. S73S77) (Fig. 4C). The 431S

section of the SONNE 102 cruise (Leth et al., 2004) presented

characteristics similar to those of SCORPIO, with a salinostad

(34.25) and pycnostad (gn 27.127.2) centered on 500700 m

depth.

The dissolved oxygen of the AAIW presented a relative

maximum (6mLL1), centered on depths similar to those of

the salinostad and pycnostad or the saline minimum (600m)

along the entire transect (Figs. 4C,5C, and7C). In the eastern endof the section (o821W), the AAIW nutrients presented a relative

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Fig. 11. Vertical distribution of silicate (mM). (A) Longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions), (B) latitudinal section off 281S



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concentration minimum (nitrate o28mM; phosphate o2.2mM;

silicate o20mM) due to the presence of the comparatively greater

ESSW concentrations in the continental slope area, which had an

effect until around 250 km from the coast (Figs. 8C, 10C, and11C).

To the west, a sort of nitratestad (2226 mM) and phosphatestad

(1.62.0mM) were found centered around 400500 m in the AAIW

(Figs. 8C and10C). Silicate increased slowly from concentrations

around 0mM at the surface to about 10mM around 600 m and thenincreased rapidly to 80mM at 1400m (Fig. 11C).

In the 281S section, the AAIW appeared as a continuous tongue

between the coast and 1001W, centered on 600 m in the coastal

area and 650 m at the western end. In this area, the AAIW mixing

ratio was between 50% and 70% and the water mass was still

located between the ESSW and the PDW east of 951W, or between

the STW and the PDW west of 951W(Fig. 6B). In the coastal area, it

was thinner (200 m) than in the oceanic area (700m).

In this section, the AAIW did not present either the salinostad

nor the pycnostad as it did at some stations in the 431S section,

but instead presented a salinity minimum (34.334.4) and a

dissolved oxygen maximum (45 mL L1) that characterized it in

the area. AAIW nutrients east of 961W were characterized by

relative minima of nitrate (2832mM) and phosphate(2.22.6mM) centered on 600 m (Figs. 4B,7B,8B, and10B). This

is because the overlying ESSW and the underlying PDW had

higher nitrate and phosphate concentrations than the AAIW,

generating the relative nutrient minimum that characterized this

water mass in the area. Silicate increased slowly from around

0mM at the surface to 10mM around 400 m, then increased rapidly

to 90mM at 1400 m (Fig. 11B).

The values of the physical and chemical variables in the

intermediate level for the SCORPIO cruise agree in general with

that observed in the longitudinal WOCE P19 section (881W)

(Tsuchiya and Talley, 1998; Talley, 20 05a) and the latitudinal

WOCE P6 (321S) (Wijffels et al., 2001;Talley, 2005b) and SONNE

102 sections (281S and 431S) (Leth et al., 2004). This implies a

certain degree of temporal and spatial stability in the area.

Nevertheless, a more detailed comparative analysis by Shaffer

et al. (2000) of the SCORPIO and SONNE 102 data showed

evidence of warming in the 431S section of up to 0.08 1C on the

neutral density levels associated with the AAIWSAAMW depth

range. In the 281S section, these authors did not detect similar

differences. Later, Schneider et al. (2005) made a TS data

comparison on the neutral density levels associated with the

AAIW depth in the WOCE P6 latitudinal section taken in 1990

off the Chilean coast and data taken in the same section during

the BEAGLE cruise in 2002. Evidence was found for warming of

0.048 1C and a salinity increase of 0.002 in the AAIW.

These authors explained this change as a possible slight shift in

the evaporation/precipitation balance in the eastern South

Pacific.

3.6. Pacific Deep Water

The PDW was found below the AAIW at depths greater than

10001200m, reaching to the bottom. Nevertheless, due to the

KRILL expedition maximum sampling depth, only the portion

above 1400 m of this water mass was analyzed. The preponderant

PDW mixing ratio was between 50% and 70% throughout the

study area (Fig. 6AC).

In the three transects, the temperature continued to decrease

slowly to 3 1C and salinity increased to 34.5 at 1400 m

(Fig. 4AC). Below 1000m depth, in the area south of 351S,

dissolved oxygen decreased to around 2.53.5 mL L1 (Figs. 4A

and 5A) and, north of 351S, increased to around 1.52.5 mL L1

(Fig. 7AC).

Nitrate and phosphate behavior was similar to but the inverse

of that of dissolved oxygen. These nutrients increased to around

38 and 2.8mM, respectively, to the south of 351S and decreased to

around 40 and 3.0mM north of 351S (Figs. 8AC and 10AC).

Silicate behavior in the area was different and, regardless of the

area, always increased in depth, reaching its highest values

(90110mM) in the north at 1400 m; values at this depth in the

south were 8090mM(Fig. 11AC).The low dissolved oxygen concentrations and high nutrient

concentrations presented by the PDW in the north of the study

area respond to the presence of the deeper OMZ remnants.

3.7. The nitrate deficit as a chemical tracer of the ESSW

Some chemical elements and compounds act conservatively in

mixing processes and, therefore, can be used to trace the

advection and mixing of a water mass that contains them. Such

is the case of cadmium (Kudo et al., 1997), tritium, freons

(Schlosser et al., 1991), and stable isotopes (Pierre et al., 1991),

among others. Moreover, chemical parameters that can behave

conservatively have also been proposed for this purpose, such aspreformed nutrients (Redfield et al., 1963;Park, 1967; Pytkowicz,

1971;Kudo et al., 1997), NO and PO (Broecker, 1974;Naqvi and

Sen Gupta, 1985; Lindegren and Anderson, 1991; Cooper et al.,

1999),N*(Gruber and Sarmiento, 1997;Deutsch et al., 2001), and

Si* (Sarmiento et al., 2004).

In oxic areas, which involve most of the ocean, nitrogen is

usually found as nitrate so that the NO3:PO4

3 molar ratio

adequately represents the Redfield ratio (N:P 16:1) in the water

column. Because nitrite can be quickly oxidized to nitrate, nitrite

concentrations are low (i.e., 0.010.75mM) in most of the ocean. In

quasi-anoxic areas (o0.2mLL1), the very low dissolved oxygen

concentrations cannot sustain the oxidation of organic matter, so

nitrate acts as an electron acceptor and is reduced to elemental

nitrogen in several steps (Thomas, 1966; Anderson et al., 1982;

Codispoti and Christensen, 1985). The first of these steps

consumes nitrate and produces nitrite that is partially accumu-

lated. This gives rise to a relative nitrate minimum and a

secondary nitrite maximum, which has been used to identify

the presence of this process in the Eastern Tropical North Pacific

(ETNP) (Brandhorst, 1959; Thomas, 1966; Codispoti and

Richards, 1976) and in the Eastern Tropical South Pacific (ETSP)

(Wooster et al., 1965; Zuta and Guillen, 1970; Daz, 1984;

Codispoti and Christensen, 1985; Silva, 1987). Denitrification

processes have also been identified in the Arabian Sea (Deuser

et al., 1978; Naqvi et al., 1982; Sen Gupta and Naqvi, 1984;

Mantoura et al., 1993).

The removal of nitrate by denitrification leaves phosphate

concentrations unaffected, thus generating an alteration in the

NO3:PO43 molar ratio of the water column. Therefore, the ratio nolonger corresponds to the Redfield ratio, as it does in oxic waters,

generating a nitrate deficit.

Silva (1987), in analyzing the nutrient contents in the waters

off northern Chile, observed that denitrification produced a

deviation of linearity in the distribution of the NO3:PO4

3 molar

ratio pairs in the water column due to anomalous pairs or

outliers that do not respond to an aerobic degradation of

the organic matter nor, therefore, to the Redfield ratio. Thus, in the

oceanographic stations where denitrification processes occur, the

NO3:PO4

3 molar ratio of the water column showed a high

deviation of the 16:1 ratios slope due to the nitrate decrease.

Nonetheless, when the outliers were not considered in the

calculation of the slope of the NO3:PO4

3 molar ratio linear

regression, it moved closer to the Redfield ratio. Silva (1987),furthermore, observed that this deviation of the NO3

:PO43 pairs

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in the area was associated with the presence of the ESSW, since

both are located in the same density levels.

The analysis of the vertical distribution of the NO3:PO4

3 molar

ratio pairs throughout the longitudinal section showed that,

towards the south, the deviation generated by denitrification in

the north remained present (Fig. 12) although the nitrate

minimum and the secondary nitrite maximum were no longer

present (Figs. 8A and9A). This deviation was considered to be afingerprint of the denitrification processes taking place off Peru

and northern Chile generated by a deficit in the nitrate

concentration. This fingerprint decreases towards the south

(Fig. 12) due to the mixing of the ESSW with SAAW and AAIW,

which are not affected by these processes.

In order to quantify the observed nitrate deficit and its

dispersion from its generation zone, the parameter N* was used

byGruber and Sarmiento (1997)andDeutsch et al. (2001)to trace

that part of the oceanic N variability due to the denitrification and

nitrogen fixation. N* values lower than 2.9 indicate a nitrate

deficit whereas values higher than 2.9 indicate excess nitrate

relative to Redfields ratio. The application of this parameter to our

data allowed the evaluation of the usefulness of the nitrate deficit

as a chemical tracer of the remnants of the denitrification

processes, as these are advected to the south and west from thedenitrification area off Peru and northern Chile.

The longitudinal section presented a core ofN* with values less

than 15mmol kg1, with minimum values less than 25mmol

kg1 associated with the cores of secondary nitrite maxima and

nitrate minima (Figs. 8A, 9A, and13A). This was expected since

the N* parameter depends on the nitrate concentrations. In this

section, the N* core extended with values lower than 5mmol

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Fig. 12. Dissolved oxygen, nitrate, nitrite, phosphate vertical profiles, and nitrate vs phosphate at selected stations in a longitudinal section off Peru and Chile (10521S;KRILL, SCORPIO, PIQUERO expeditions). The values in open circles were not considered in the regression calculation.


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kg1 beyond the nitrite maximum and nitrate minimum area,

decreasing toward the north and south and covering the area

between 101S and 401S, centered on a depth of 100200 m, which

also corresponds to the depth of ESSW core (Fig. 13A).

In the 281S section, where neither perceptible secondary nitrite

maxima nor nitrate minima were recorded, three cores ofN* less

than 15mmol kg1 were found (Figs. 8B, 9B, and 13B). Two of

these were in the most coastal area (731W and 761W) and one

was oceanic (901W); the three were associated with the presence

of subsurface salinity maxima and dissolved oxygen minima

(Figs. 4B and7B) typical of the ESSW (Fig. 6C).

In the 431S section, where cores of secondary nitrite maximaand nitrate minima were also absent, only a remnant of the N*

core, coming from the north, was observed (o5mmolkg1)

(Figs. 8C, 9C, and 13C). This maximum was found along the

continental slope, associated with the presence of the remnants of

the salinity maximum and dissolved oxygen minimum (Figs. 4C

and7C) of the ESSW (Fig. 6C).

If the participation percentage distributions of the different

water masses in the mixture are compared with the N* values less

than 5mmol kg1 (Figs. 6A vs13A, 6B vs13B,6C vs13C), they

coincide with the distribution of ESSW values over 50% participa-

tion in the three transects.

In order to analyze the behavior ofN* as a conservative tracer

of the ESSW, the pairs N* vs %ESSW values, corresponding tothe ESSW core, were graphed for each oceanographic station

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Fig. 13. Vertical distribution of the nitrate deficit (N*) in: (A) a longitudinal section off Peru and Chile (10521S; KRILL, SCORPIO, PIQUERO expeditions). Dotted line

corresponds to 50% ESSW mixing ratio; (B) a latitudinal section at 28 1S (SCORPIO expedition). Dotted line corresponds to 50% ESSW mixing ratio; (C) a latitudinal section at

431S (SCORPIO expedition). Dotted line corresponds to 50% ESSW mixing ratio; and (D) lineal association between N* and the maximum participation percentage in the

ESSW core. The stations with %ESSW greater than 95% (to the right of the dashed line) were not considered in the linear regression calculation.


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(Fig. 13D). Those pairs in which the ESSW participation was over

95% deviated widely from the regression line associatingN* with

%ESSW.

These anomalous pairs corresponded to stations off Peru and

northern Chile, where denitrification, a non-conservative chemi-

cal process, takes place.

South of 251S, in the longitudinal and both latitudinal sections,

N* behaved conservatively since the N* vs %ESSW relationship inthe ESSW core presented a significant, inverse, linear association

(r2 0.91) (Fig. 13D). The same occurs ifN* vs salinity is plotted in

the subsurface salinity core and, in this case, the separation occurs

at salinities over/under 34.8 (not shown).

A similar situation can be observed in the N* vsSrelationship

at the surface ofsy 26.2 off the coast of Peru and northern and

central Chile, presented by Deutsch et al. (2001), where the

separation of the zones also takes place at salinities over/under

34.8. This isopycnal is located around 100150 m depth and, off

Peru and Chile, corresponds to the location of the upper part of the

ESSW.

Therefore, we concluded that the nitrate deficit, represented by

N* core values less than 5mmolkg1, could be used as a

conservative chemical tracer of the ESSW off central and southernChile, as is salinity.

Acknowledgments

The authors would like to thank the Eastern South Pacific

Oxygen Minimum Zone program for having considered the

present work for their publication and Miss Yenny Guerrero for

her help with the drawings. Prof. Nelson Silva is grateful to Dr.

Tarsicio Antezana for the invitation to participate in the KRILL Leg

4 cruise and for access to the cruises oceanographic data.

References

Ahumada, R., Matrai, P., Silva, N., 1991. Phytoplankton biomass distribution andrelationship to nutrient enrichment during an upwelling event off ConcepcionBay Chile. Boletn de la Sociedad Biologica de Concepcion 62, 719.

Anderson, J.J., Okubo, A., Robbins, A.S., Richards, F.A., 1982. A model for nitrite andnitrate distributions in oceanic oxygen minimum zones. Deep-Sea Research 29(9A), 11131140.

Blanco, J.L., Thomas, A.C., Carr, M.E., Strub, P.T., 2001. Seasonal climatology ofhydrographic conditions in the upwelling region off northern Chile. Journal ofGeophysical Research 106 (C6), 1145111467.

Brandhorst, W., 1959. Nitrification and denitrification in the Eastern Tropical NorthPacific. Journal Conseil International pour lExploration de La Mer 25 (1), 320.

Broecker, W.S., 1974. NO, a conservative water mass tracer. Earth and PlanetaryScience Letters 23, 100107.

Carpenter, J.H., 1965. The Chesapeake Bay Institute technique for the Winklerdissolved oxygen method. Limnology and Oceanography 10, 141143.

Codispoti, L.A., 1981. Temporal nutrient variability in three different upwellingregions. In: Richard, F.A. (Ed.), Coastal Upwelling. American Geophysical Union,Washington, DC, pp. 209220.

Codispoti, L.A., Christensen, J.P., 1985. Nitrification, denitrification and nitrousoxide cycling in the Eastern tropical South Pacific Ocean. Marine Chemistry 16,227300.

Codispoti, L.A., Packard, T.T., 1980. Denitrification rates in the eastern TropicalSouth Pacific. Journal of Marine Research 38 (3), 453477.

Codispoti, L.A., Richards, F.A., 1976. An analysis of the horizontal regime ofdenitrification in the eastern tropical North Pacific. Limnology and Oceano-graphy 21 (3), 379388.

Cooper, L.W., Cota, G.F., Pomeroy, L.R., Grebmeier, J.M., Whitledge, T.E., 1999.Modification of NO, PO, and NO/PO during flow across the Bering and Chukchishelves: implications for use as Arctic water mass tracers. Journal ofGeophysical Research 104 (C4), 78277836.

Cucalon, E., 1983. Temperature, salinity and water mass distribution off Ecuadorduring an El Nino event in 1976. Revista de Ciencias Marinas y Limnologa 2(1), 125.

Davila, P.M., Figueroa, D., Muller, E., 2002. Freshwater input into the coastal oceanand its relation with the salinity distribution off austral Chile (35551S).Continental Shelf Research 22, 521534.

Deacon, G.E.R., 1977. Comments on a counterclockwise circulation in the Pacificsubantarctic sector in the Southern Ocean suggested by Mc Ginnis. Deep-SeaResearch 24, 927930.

De Pol-Holz, R., Ulloa, O., Lamy, F., Dezileau, L., Sabatier, P., Hebbeln, D., 2007. LateQuaternary variability of sedimentary nitrogen isotopes in the eastern SouthPacific Ocean. Paleoceanography 22, PA2207.

Deuser, W.G., Ross, E.H., Mlodzinska, Z.J., 1978. Evidence for and rate ofdenitrification in the Arabian Sea. Deep-Sea Research II 25, 431445.

Deutsch, C., Gruber, N., Key, R.M., Sarmiento, J.L., 2001. Denitrification andN2 fixation in the Pacific Ocean. Global Biogeochemical Cycles 15 (2),483506.

Daz, M., 1984. Distribucion de fosfatos, nitratos y nitritos en una seccio n frente a

Iquique (20116

0

S), December 1982. Investigacion Pesquera 31, 103108 (withEnglish Abstract).Escribano, R., Daneri, G., Faras, L., Gallardo, V., Gonzalez, H., Gutierrez, D., Lange, C.,

Morales, C., Pizarro, O., Ulloa, O., Braun, M., 2004. Biological and chemicalconsequences of the 19971998 El Nino in the Chilean coastal upwellingsystem: a synthesis. Deep-Sea Research II 51, 23892411.

Fuenzalida, R., Blanco, J.L., Vega, C., 2000. Fronteras de la corriente de Humboldt ymasas de agua entre el continente e Isla de Pascua. Taller de resultados delCrucero Cimar-Fiordo 5. Libro de Resumenes. Comite Oceanografico Nacional,Valparaso, Chile, pp. 2432 (in Spanish).

Gonzalez, H.E., Pages, F., Sobarzo, M., Escribano, R., 2002. Effects of the 1997/1998El Nino on the oceanographic conditions and zooplankton communitystructure in the coastal upwelling system off northern Chile. InvestigacionesMarinas (extended abstract) 30 (1), 112114.

Gruber, N., Sarmiento, J.L., 1997. Global patterns of marine nitrogen fixation anddenitrification. Global Biogeochemical Cycles 11 (2), 235266.

Gunther, E.R., 1936. A report on oceanographical investigations in the Peru CoastalCurrent. Discovery Report 13, 107276.

Johnson, R.E., 1973. Antarctic intermediate water in the South Pacific Ocean. In:

Fraser, R. (Ed.), Oceanography of the South Pacific 1972. New Zealand NationalCommission for UNESCO, Wellington, pp. 5569.

Kudo, I., Kokubun, H., Matsunaga, K., 1997. Preformed phosphate and cadmium inthe Pacific Ocean. In: Tsunogai, S. (Ed.), Biogeochemical Processes in the NorthPacific. Japan Marine Science Foundation, Tokyo, pp. 156161.

Leth, O., Shaffer, G., Ulloa, O., 2004. Hydrography of the eastern South PacificOcean: results from the Sonne 102 cruise, MayJune 1995. Deep-Sea ResearchII 51, 23492369.

Lindegren, R., Anderson, L.G., 1991. NO as a conservative tracer in the WeddellSea. Marine Chemistry 35, 179187.

Mamayev, O.,1975. TemperatureSalinity Analysis of World Ocean Waters, ElsevierOceanography Series, vol. 11. Elsevier, Amsterdam.

Mantoura, R.F.C., Law, C.S., Owens, N.J.P., Burkil, P.H., Woodward, E.M.S., Howland,R.J.M., Llewellyn, C.A., 1993. Nitrogen biogeochemical cycling in the north-western Indian Ocean. Deep-Sea Research II 40, 651671.

McCartney, M.S., 1977. Subantarctic mode water. In: Angel, M. (Ed.), A Voyage ofDiscovery. Pergamon Press, Oxford and New York, pp. 103119.

Morales, C.E., Blanco, J.L., Braun, M., Reyes, H., Silva, N., 1996. Chlorophyll-adistribution and associated oceanographic conditions in the upwelling offnorthern Chile during winter and spring 1993. Deep-Sea Research I 43 (3),267289.

Morales, C.E., Blanco, J.L., Braun, M., Silva, N., 2001. Chlorophyll-a distribution andmesoscale physical processes in upwelling and adjacent oceanic zones offnorthern Chile (summerautumn 1994). Journal of the Marine BiologicalAssociation of the United Kingdom 81, 193206.

Naqvi, S.W., Sen Gupta, R., 1985. NO, a useful tool for the estimation of nitratedeficits in the Arabian Sea. Deep-Sea Research 32 (6), 665674.

Naqvi, S.W., Noronha, R.J., Gangadhara Reddy, C.V., 1982. Denitrification in theArabian Sea. Deep-Sea Research 29 (4A), 459469.

Neshyba, S., Fonseca, T., 1980. Evidence for a counterflow to West Wind Drift offSouth America. Journal Geophysical Research 85, 48884892.

NOAA, 2006. Equatorial Southern Oscillation Index. WWW Page, /http://www.cpc.ncep.noaa.gov/data/indices/reqsoi.forS (Reviewed 10 October 2006).

Palma, S., Silva, N., 2004. Distribution of siphonophores, chaetognaths, euphausiidsand oceanographic conditions in the fjords and channels of southern Chile.Deep-Sea Research II 51, 513535.

Park, P.K., 1967. Nutrient regeneration and preformed nutrients off Oregon.

Limnology and Oceanography 12 (2), 353357.Pierre, C., Vergnaud-Grazzini, C., Faugeres, J.C., 1991. Oxygen and carbon stable

isotope tracers of the water masses in the Central Brazil Basin. Deep-SeaResearch 38 (5), 597606.

Piola, A.R., Georgi, D.T., 1982. Circumpolar properties of Antarctic IntermediateWater and Subantartic Mode Water. Deep-Sea Research 29 (6a), 687711.

Pytkowicz, R.M., 1971. On the apparent oxygen utilization and the preformedphosphate in the oceans. Limnology and Oceanography 16 (1), 3942.

Redfield, A.C., Ketchum, B.H., Richards, F.A., 1963. The influence of organismson the composition of sea-water. In: Hill, M.N. (Ed.), The Sea. Ideasand Observations on Progress in the Study of the Seas. Wiley, New York,pp. 2677.

Reid, J.L., 1962. On circulation phosphate-phosphorus content, and zooplanktonvolumes in the upper part of the Pacific Ocean. Limnology and Oceanography 7,237306.

Reid, J.L., 1965. Intermediate Waters of the Pacific Ocean. The Johns HopkinsOceanographic Studies, vol. 2. The Johns Hopkins Press, Baltimore.

Reid, J.L., 1969. Sea-surface temperature, salinity, and density of the Pacific Oceanin summer and in winter. Deep-Sea Research 16, 215224.

Reid, J.L., 1973a. The shallow salinity minimum of the Pacific Ocean. Deep-SeaResearch 20, 5158.

ARTICLE IN PRESS

http://www.cpc.ncep.noaa.gov/data/indices/reqsoi.forhttp://www.cpc.ncep.noaa.gov/data/indices/reqsoi.forhttp://www.cpc.ncep.noaa.gov/data/indices/reqsoi.forhttp://www.cpc.ncep.noaa.gov/data/indices/reqsoi.for

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Reid, J.L., 1973b. Transpacific hydrographic sections at lats. 431S and 281S: theSCORPIO Expedition-III. Upper water and a note on southward flow at mid-depth. Deep-Sea Research 20, 3949.

Robles, F., Alarcon, E., Ulloa, A., 1975. Las masas de agua en la region norte de Chiley sus variaciones en un perodo fro (1967) y en perodos calidos (1969,19711973). FAO Fisheries Report 185, 94196 (in Spanish).

Rojas, R., Silva, N., 1996. Atlas Oceanografico de Chile (181210S a 501000S), vol. 1.Servicio Hidrografico y Oceanografico de la Armada de Chile, Valparaso, Chile(in Spanish).

Ruddick, B., 1983. A practical indicator of the stability of the water column todouble-diffusive activity. Deep-Sea Research 30, 11051107.Sarmiento, J.L., Gruber, N., Brzezinski, M.A., Dunne, J.P., 2004. High-latitude

controls of thermocline nutrients and low latitude biological productivity.Nature 427, 5660.

Schlosser, P., Bullister, J.L., Bayer, R., 1991. Studies of deep water formation andcirculation in the Weddell Sea using natural and anthropogenic tracers. MarineChemistry 35, 97122.

Schneider, W., Fuenzalida, R., Rodrguez-Rubio, E., Garces-Vargas, J., Bravo, L., 2003.Characteristics and formation of eastern South Pacific Intermediate Water.Geophysical Research Letters 32, 1460214605.

Schneider, W., Fukasawa, M., Uchida, H., Kawano, T., Kaneko, I., Fuenzalida, R.,2005. Observed property changes in the eastern South Pacific AntarcticIntermediate Water. Geophysical Research Letters 32, 1460214605.

Scripps Institution of Oceanography, 1969. Physical and chemical data fromSCORPIO Expedition in the South Pacific Ocean. USNS Eltain Cruises 28 and 29,12 March21 July 1967. SIO Reference 69-15; WHOI Reference 69-56, La Jolla,CA, 89pp.

Scripps Institution of Oceanography, 1974. Data report physical and chemical data.

PIQUERO Expedition, 16 December 196816 April 1969. SIO Reference 74-27,59pp.

Sen Gupta, R., Naqvi, S.W., 1984. Chemical oceanography of the Indian Ocean, northof the Equator. Deep-Sea Research 31 (68), 671706.

Shaffer, G., Leth, O., Ulloa, O., Bendtsen, J., Daneri, G., Dellarossa, V., Hormazabal, S.,Sehlsetedt, P.I., 2000. Warming and circulation change in the eastern SouthPacific Ocean. Geophysical Research Letters 27, 12471250.

Sievers, H., Silva, N., 1975. Masas de agua y circulacion en el Oceano Pacfico SudOriental. Latitudes 181331S. (Operacion Oceanografica MARCHILE VIII).Ciencia y Tecnologa del Mar 1, 767 (with English Abstract).

Silva, N., 1977. Water mass structure and circulation off southern Chile. MasterThesis, School of Oceanography, Oregon State University, USA, 83pp. (partiallypublished).

Silva, N., 1987. Contenido de sales nutrientes de las aguas de la regio n norte deChile (Crucero MARCHILE XII-ERFEN III). Ciencia y Tecnologa del Mar 11,95117 (with English Abstract).

Silva, N., Fonseca, T.R., 1983. Geostrophic component of the oceanic flow offnorthern Chile. In: Arana, P. (Ed.), Recursos Marinos del Pacfico. Escuela deCiencias del Mar, Universidad Catolica de Valparaso, Valparaso, Chile, pp.5970.

Silva, N., Konow, D., 1975. Contribucion al conocimiento de las masas de agua en elPacfico Sudoriental Expedicion Krill. Crucero 34 JulyAugust 1974. Revista dela Comision Permanente Pacfico Sur 3, 6375 (with English Abstract).

Silva, N., Neshyba, S., 1977. Corrientes superficiales frente a la costa austral deChile. Ciencia y Tecnologa del Mar 3, 3742 (with English Abstract).

Silva, N., Neshyba, S., 1979. On the southernmost extension of the PeruChileUndercurrent. Deep-Sea Research 26A, 13871393.

Silva, N., Neshyba, S., 1980. Masas de agua y circulaciongeostrofica frente a la costade Chile Austral. Serie Cientfica. Instituto Antartico Chileno 25/26, 532 (withEnglish Abstract).

Silva, N., Valdenegro, A., 2003. Evolucion de un evento de surgencia frente a puntaCuraumilla. Valparaso. Investigaciones Marinas 31 (2), 7389 (with EnglishAbstract).

Silva, N., Calvete, C., Sievers, H., 1997. Caractersticas oceanograficas fsicas yqumicas de canales australes chilenos entre Puerto Montt y laguna San Rafael(Crucero Cimar Fiordo 1). Ciencia y Tecnologa del Mar 20, 23106 (with

English Abstract).Strickland, J.D.H., Parsons, T.R., 1972. A Practical Handbook of Seawater Analysis.Fisheries Research Board of Canada, Ottawa.

Strub, P., Mesas, J., Montecino, V., Rutllant, J., Salinas, S., 1998. Coastal oceancirculation off western South America. In: Robinson, A., Brink, K. (Eds.), TheSea, The Global Coastal Ocean, vol. 11. Wiley, New York, pp. 272313.

Talley, L., 2005a. WOCE P19 vertical sections. WWW Page, /http://www-word.ucsd.edu/whp_atlas//pacific/p19/sections/printatlas/printatlas.htmS(Reviewed 10 March 2005).

Talley, L., 2005b. WOCE P06 vertical sections. WWW Page, /http://www-word.ucsd.edu/whp_atlas//pacific/p06/sections/printatlas/printatlas.htmS(Reviewed 10 March 2005).

Talley, L., 2005c. WOCE P17 vertical sections. WWW Page, /http://www-word.ucsd.edu/whp_atlas//pacific/p19/sections/printatlas/printatlas.htmS(Reviewed 10 March 2005).

Thomas, W.H., 1966. On denitrification in the northeastern Tropical Pacific Ocean.Deep-Sea Research 13, 11091114.

Tsuchiya, M., Talley, L., 1996. Water-property distribution along an eastern Pacifichydrographic section at 1351W. Journal of Marine Research 54, 541564.

Tsuchiya, M., Talley, L., 1998. A Pacific hydrographic section at 881W: water-property distribution. Journal of Geophysical Research 13 (C6), 1289912918.

Ulloa, O., Escribano, R., Hormazabal, S., Quinones, R.A., Ramos, M., Gonzalez, R.R.,2001. Evolution and biological effects of the 19971998 El Nino in northernChile. Geophysical Research Letters 28 (8), 15911594.

Weiss, W.J., 1970. The solubility of nitrogen, oxygen and argon in water and seawater. Deep-Sea Research 17, 721735.

Wijffels, S.E., Toole, J.M., Davis, R., 2001. Revisiting the South Pacific subtropicalcirculation: a synthesis of World Ocean Circulation Experiment observationsalong 321S. Journal of Geophysical Research 106, 1948119513.

Wooster, W.S., Gilmartin, M., 1961. The PeruChile undercurrent. Journal of MarineResearch 19 (3), 97122.

Wooster, W.S., Chow, T.J., Barrett, I., 1965. Nitrite distribution in Peru Currentwaters. Journal of Marine Research 23 (3), 210221.

Wyrtki, K., 1963. The horizontal and vertical field of motion in the Peru Current.Bulletin of the Scripps Institution of Oceanography 8 (4), 313346.

Wyrtki, K., 1967. Circulation and water masses in the eastern equatorial PacificOcean. International Journal of Oceanography and Limnology 1 (2), 117147.

Wyrtki, K., 1968. Water masses in the oceans and adjacent seas. In: InternationalDictionary of Geophysics. Pergamon Press, Tarrytown, NY, pp. 111.

Yanez, E., Gonzalez, A., Barbieri, M.A., 1995. Sea surface thermal structureassociated to the space-temporal distribution of sardines and anchovy innorthernChile. Investigaciones Marinas 23, 123147.

Yanez, E., Barbieri, M.A., Silva, C., Nieto, K., Espndola, F., 2001. Climate variabilityand pelagic fisheries in northern Chile. Progress in Oceanography 49, 581596.

Zuta, S., Guillen, O., 1970. Oceanografa de las aguas costeras del Peru. BoletnInstituto del Mar del Peru 2 (5), 157324.

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